A light emitting diode (“LED”) can provide light in a more efficient manner than an incandescent light source and/or a fluorescent light source. The relatively high efficiency associated with LEDs has created an interest in using LEDs to displace conventional light sources in a variety of lighting applications. For example, LEDs are being used in traffic lighting, residential lighting, automobile lighting systems, flashlights, and to illuminate cell phone keypads and displays.
LED lighting circuits that use standard AC input power (“AC mains”) generally include an input power circuit that converts AC input power to a rectified DC power signal, circuitry or components to filter or reduce the voltage ripple component of the DC power signal, and circuitry to create a current from the DC power signal and control its peak current flow to the LED load. Some circuits also include capacitors to act as an energy storage buffer, providing the difference between the varying input voltage of the AC mains and the relatively constant power consumed by the LED load. A typical LED load is an LED mesh circuit, well known in the prior art, which can include a number of LEDs in series, parallel branches of LEDs in series, or combinations thereof.
The reliability of an LED lighting circuit can be improved by eliminating the components with the lowest Mean Time Between Failures (“MTBF”) of the individual components that make up the circuit. LEDs are very high-reliability components, which have a typical Mean Time Between Failures (“MTBF”) in the range of 100,000 to 1,000,000 hours, whereas devices that store energy, such as capacitors, are the lowest-reliability components. Electrolytic capacitors, which are heavily used in industry, have a typical MTBF in the range of 15,000 to 50,000 hours.
Prior art devices consume a significant amount of power to operate their ripple voltage reducing circuitry and capacitive coupling circuitry, which subtracts from the power that can be delivered to the LED load. The addition of capacitor, inductor, and heatsink components also adds to complexity and cost. Because prior art LED lighting circuits typically utilize combinations of capacitor, inductor, and heatsink components to reduce the ripple voltage of the rectified DC signal, and capacitors to provide an energy buffer between the varying input voltage of the AC mains and the near constant power consumed by the LED load, such circuits have their reliability limited by the MTBF of their capacitors, do not drive an increasing number of LEDs with increasing AC mains voltage while also maintaining low current to the LED load, are expensive, and can be complicated to build and package. The present invention addresses the above-noted shortcomings of the prior art while providing additional benefits and advantages.